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For decades, running enthusiasts have speculated that women were better suited for distance running than men because of their higher body-fat ratios  hence a greater emergency fuel store. A look at marathon times between men and women appears to bolster the theory. As more and more women have taken up distance running, the gap between the world's best men's marathon time and the world's best women's time has steadily narrowed. Tim Noakes, professor of exercise and sports science at the University of Cape Town, explains surprising recent findings about a popular athletic debate.

Q: Will women ever run a marathon faster than men?

A: Unfortunately the answer is, unless they become men, no, they
won't.

There was some speculation many years ago, in the 1970s, that because women had greater fat stores, they would outlast men in long-distance events. We have a famous race in South Africa, the 90-km (56-mi) Comrades marathon. Some years ago we wrote a paper in which we made the case that if a man and a woman could run a [standard 42-km (26-mi)] marathon in the same time, the woman would likely win the longer Comrades race by about an hour. She'd be about an hour faster.

Then we realized what the problem was. When you look at most recreational runners, men and women are not the same size. If you compare a man and a woman both running three-hour marathons, for example, you generally find that the man is about 10 kg (22 lbs) heavier, or maybe even more. But when we measured the world's best athletes, we found that the men and the women were roughly the same weight. So, the female world-record holder in the marathon is about 54 kg (119 lbs) and the male world-record holder is about 56 kg (124 lbs). If you don't match for weight, then women get a huge advantage over longer distances, simply because they have less mass to move around. But once you match for weight, the men run about 10% faster. We've really shown now that at any distance between 100 m up to 1,000 km (620 mi), women are consistently somewhere between 9% and 11% slower than men. We expect that until women can run 100 m as fast as men, women won't beat men even at 1,000 km.

That's probably a testosterone-dependent effect. Running is all about getting your foot off the ground. You've just got 200 milliseconds or 300 milliseconds to apply the force to push you through the air, so you need an enormously strong leg. Now Paula Radcliffe, [the world-record holder in the women's marathon], is 54 kg. At her 54 kg, she just doesn't have the muscle power that the men have. I think that's the differentiating factor. You have to have testosterone in your body for 20 years to develop the strength that the Kenyan male runners have. I suppose if you could genetically engineer women  if you could put men's muscles into them  they could be as fast. Who knows? Otherwise, even using steroids, women are not as fast as men.